1. Field of the Invention
The present invention relates in general to electromagnetic induction heating cookers, and more particularly to an overheat prevention circuit for an electromagnetic induction heating cooker which is capable of preventing a fire or a burn resulting from overheating of a top plate which may be generated due to a fault of the user or a malfunction of the appliance itself.
2. Description of the Prior Art
Generally, an electromagnetic induction heating cooker comprises a top plate disposed over a heating coil, on which an object (i.e., a cooking container) to be heated is laid, temperature sensing means for sensing a temperature of the object, high-frequency power generation means for generating a high-frequency magnetic field to the heating coil to induction-heat the object, and control means for controlling the high-frequency power generation means in accordance with the temperature of the object sensed by the temperature sensing means.
As the electromagnetic induction heating cooker is operated under the control of the user, the object laid on the top plate is heated. At this time, the temperature sensing means senses the temperature of the heated object through the top plate on which the object is laid. The sensed temperature from the temperature sensing means is applied to the control means. If the sensed temperature is greater than or equal to a predetermined reference value, the control means stops the operation of the high-frequency power generation means.
One example of such an electromagnetic induction heating cooker is disclosed in Japanese Patent Laid-open Publication No. Sho 61-230288 entitled "INDUCTION HEATING COOKER", and is shown in FIG. 2, herein.
In the electromagnetic induction heating cooker of the above patent, as shown in FIG. 2, an object. (cooking container) 3 to be heated is laid on a top plate 2 disposed in a cooking base body 1, and is induction-heated by a high-frequency magnetic field. A temperature sensor 4 acts to sense a temperature of the object 3 on the top plate 2.
The conventional electromagnetic induction heating cooker in FIG. 2 is adapted to prevent a fire and the like which may take place as an actual temperature of the heated object 3 becomes higher than the temperature sensed by the temperature sensor 4 at an initial state of the heating. To this end, the conventional electromagnetic induction heating cooker in FIG. 2 comprises temperature over-rise prevention means for stopping the heating operation if the temperature sensed by the temperature sensor 4 reaches a predetermined reference value, and control means for reducing the heating output for a predetermined time period at the initial state of the heating.
In FIG. 2, the temperature over-rise prevention means and the control means are provided on a control circuit board 8. The reference numerals 5, 6, 7 and 9, not described, designate a heating coil, an inverter circuit, a power transformer and a cooling fan, respectively.
The above-mentioned conventional electromagnetic induction heating cooker has the effect of preventing overheating, more particularly the occurrence of the fire at the initial state of the heating operation. However, the conventional electromagnetic induction heating cooker has a disadvantage in that a fire or a burn may take place due to overheating of the top plate resulting from a malfunction of a component in the appliance such as the temperature sensor. Also, the electromagnetic induction heating cooker cannot be used as long as the reliability of the associated circuitry is not 100% assured on the basis of a control circuit failure mode effect analysis (FMEA) of an UL standard about safety, which has recently been enforced in U.S.A.